This invention relates to an improved mothod of and apparatus for transfer printing, from an image forming surface to the surface of a recording sheet, a toner image obtained by developing an electrostatic latent image with a powder developing agent.
There are various types of transfer printing methods known in the art. In one widely practised method, corona transfer printing is effected under the influence of corona discharge. This method has a disadvantage in that the deterioration of a photosensitive body is speeded up and the service life thereof is reduced. An additional disadvantage is that means for feeding recording sheets must be provided separately. In another method known in the art, transfer printing is effected by using a metallic roller on which a bias voltage is impressed. When this method is used, a discharge occurring between the photosensitive body and very small projecting portions of the metallic roller on which a bias voltage is impressed tends to damage the photosensitive body. Moreover, owing to the fact that the width over which the photosensitive body and the metallic roller are brought into contact with each other is small, satisfactory results are not obtained in effecting transfer printing. Furthermore, since the recording sheet is abruptly separated from the photosensitive body after transfer printing of a toner image is effected, an electric force acts between the toner particles on the recording sheet and the electric charge remaining on the photosensitive body, with the result that there is the danger of the toner image on the recording sheet being disturbed. In still another method, an electrically conductive rubber roller, on which a bias voltage is impressed, is used for performing transfer printing. This method also has the disadvantage of a discharge occurring between the photosensitive body and very small projecting portions of the electrically conducting rubber roller on which a bias voltage is impressed.
In order to obviate the aforementioned disadvantages of various transfer printing methods, a transfer printing method utilizing a transfer printing belt is known.